1. Field of Invention
The present invention relates to a motor and a motor speed control system.
2. Related Art
In the prior art, many signal lines are coupled between a motor and a control device for controlling the motor to rotate, and the connections therebetween are very complicated. For example, a controller for controlling a brushless motor for driving a fan, is shown in FIG. 1. Herein, a positive power signal line 161 and a negative power signal line 162 are coupled between a controller 12 and a brushless motor 14, so that the controller 12 and the brushless motor 14 are electrically connected to each other. In addition, a speed-control signal line 163 is for transmitting a speed-control signal generated by the controller 12 to the brushless motor 14 so that a processor (not shown) inside the brushless motor 14 can drive the brushless motor 14 to rotate at a specific speed according to the speed-control signal of the controller 12. A rotating speed feedback signal line 164 coupled between the controller 12 and the brushless motor 14 is for transmitting a feedback signal generated by the processor inside the brushless motor 14 to the controller 12. Thus, the controller 12 can identify whether the rotating speed of the brushless motor 14 at each timing can satisfy the setting of the rotating speed corresponding to the speed-control signal at the timing or not according to the received feedback signal.
Consequently, in order to precisely monitor the rotation of the brushless motor 14, at least four signal lines, such as the positive power signal line 161, the negative power signal line 162, the speed-control signal line 163 and the speed feedback signal line 164, have to be coupled between the brushless motor 14 and the controller 12 for controlling the motor. The speed-control signal line 163 and the speed feedback signal line 164 are respectively for transmitting the signal from the controller 12 to the brushless motor 14 and the signal from the brushless motor 14 to the controller 12. That is, the speed-control signal line 163 and the speed feedback signal line 164 are signal lines for one-way transmission. However, the control signals between the controller 12 and the brushless motor 14 include not only the speed-control signal and the feedback signal, but also a driving signal, a timing signal and other signals. In order to transmit these signals, more than four signal lines are coupled between the controller 12 and the brushless motor 14 in the practical application. Therefore, the overall circuit architecture is very complicated, and the element cost, assembling time and device error rate are inversely influenced.